Mixed phosphates of lanthanum and/or cerium, doped with terbium (usual acronym “LAP”), are well-known phosphor compositions. A LaPO4:Ce, Tb phosphor composition is known as green phosphor (LAP) as it emits a bright green light when it is irradiated by certain high-energy radiation having wavelengths below the visible range. This property is advantageously used on an industrial scale, for example, in trichromatic fluorescent lamps, backlighting systems for liquid crystal displays and in plasma systems.
Various synthesis methods have been developed to maximize the efficiency of LAP phosphor. Some of the synthesis methods improve crystallinity of LAP phosphor thereby enhancing the efficiency. Some other synthesis methods optimize the particle size distribution and morphology of phosphor particles in order to get uniform coating during lamp coating.
However, a problem still unaddressed is of their particularly high cost, linked especially to the use of terbium. A core-shell approach for phosphor has been proposed to decrease the concentration of terbium and thus to lower the cost of LAP. Hence, it is desirable to develop core-shell phosphors to meet the existing need for inexpensive, high quality phosphors. Coating of relatively inexpensive core with expensive shell materials can help lower the cost of phosphor as well as the cost of manufacturing fluorescent lamps.